The leader of the Roman Catholic Church in England and Wales has condemned plans to make it easier for lesbian couples to use IVF to become parents.
Cardinal Cormac Murphy-O'Connor opposes the proposed Bill
In a Times letter, Cardinal Cormac Murphy-O'Connor said the plans were "profoundly wrong" and undermined "the place of the father in a child's life".
But campaign group Stonewall said the move was a "logical and timely step".
The measures are contained in the Human Fertilisation and Embryology Bill, being debated in the Lords later.
The Bill includes recognition of same-sex couples as legal parents and would remove the current requirement on IVF clinics to be sure that a father is involved in the upbringing of any child created after he donates sperm.
MPs have previously called for an end to the right of fertility clinics to refuse treatment to single women and lesbians.
Cardinal Murphy-O'Connor wrote: "The bill proposes to remove the need for IVF providers to take into account the child's need for a father when considering an IVF application and to confer legal parenthood on people who have no biological relationship to a child born as a result of IVF.
"This radically undermines the place of the father in a child's life, and makes the natural rights of the child subordinate to the desires of the couple. It is profoundly wrong."
But Ruth Hunt, of gay rights campaign group Stonewall, said the plans did not involve "denigrating the principle of fatherhood".
"This is a very logical and timely step to ensure that a child can have two parents from the moment of conception and that is safeguarded throughout their upbringing," she said.
Cardinal Murphy-O'Connor has called on the government to allow Labour members in both houses to have a free vote on the issue - as opposition members already do.
Family campaigners are also stepping up their opposition to the Bill, with former Tory leader Iain Duncan Smith warning it would be a "nail in the coffin" of the traditional family and "another blow" against fatherhood.
Stonewall dismissed his concerns, saying that, at a time when three million children were growing up in single parent households in the UK, it would give more children the chance of a two-parent home.
The Bill would also open the door to experiments involving human-animal hybrid embryos, including "cytoplasmic" embryos, which are 99.9% human, and "true hybrids", carrying both human and animal genes.
In addition, "chimeras" made of a mosaic-like mix of cells from different species, and "human transgenic embryos" - human embryos modified with animal DNA - will be allowed under licence.
It also includes a ban on sex-selection for non-medical reasons.
Both pro-choice and anti-abortion campaigners are likely to use the Bill to try to change the law on abortions.